Fish are aquatic vertebrates that are typically cold-blooded; covered with scales, and equipped with two sets of paired fins and several unpaired fins. Fish are abundant in the sea and in fresh water, with species being known from mountain streams (e.g., char and gudgeon) as well as in the deepest depths of the ocean (e.g., gulpers and anglerfish). They are of tremendous importance as food for people around the world, either collected from the wild (see fishing) or farmed in much the same way as cattle or chickens (see aquaculture). Fish are also exploited for recreation, through angling and fishkeeping, and fish are commonly exhibited in public aquaria. Through the ages, many cultures have featured fish in their legends and myths, from the "great fish" that swallowed Jonah the Prophet through to the half-human, half-fish mermaid around which books and movies have been centred (e.g., Splash (film)). Fish have been used as symbols in many different ways, from the ichthys used by early Christians through to the allegorical use of a marlin in Ernest Hemingway's novel, The Old Man and the Sea
What is a fish?
The term "fish" is most precisely used to describe any non-tetrapod chordate, i.e., an animal with a backbone but lacking four limbs (or having ancestors that had four limbs). Unlike groupings such as birds or mammals, fish are not a single clade but a paraphyletic collection of taxa including hagfishes, lampreys, sharks, rays, lungfishes and coelacanths, sturgeons, gars, and advanced ray-finned fishes. [1]
A typical fish is cold-blooded; has a streamlined body that allows it to swim rapidly; extracts oxygen from the water using gills; has two sets of paired fins, one or two dorsal fins, an anal fin, and a tail fin; has jaws; has skin that is covered with scales; and lays eggs that are fertilised externally.
Fish come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. Their leaf-like appendages enable them to blend in with floating seaweed
However, to each of these there are exceptions. Tuna and some species of sharks are warm-blooded, and able to raise their body temperature significantly above that of the ambient water surrounding them. [2] Streamlining and swimming performance varies from highly streamlined and rapid swimmers which are able to reach 10-20 body-lengths per second (such as tuna, salmon, and jacks) through to slow but more manoeuvrable species such as eels and rays that reach no more than 0.5 body-lengths per second. [3] Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Lungfish have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many catfish, such as Corydoras extract oxygen via the intestine or stomach. [4] Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms as seahorses, pufferfish, anglerfish, and gulpers. Similarly, the surface of the skin may be naked (as in moray eels), or covered with scales of a variety of different types usually defined as placoid (typical of sharks and rays), cosmoid (fossil lungfishes and coelacanths), ganoid (various fossil fishes but also living gars and bichirs, cycloid, and ctenoid (these last two are found on most bony fish. [5] There are even fishes that spend most of their time out of water. Mudskippers feed and interact with one another on mudflats and are only underwater when hiding in their burrows. [6] The catfish Phreatobius cisternarum lives in waterlogged leaf litter [7], [8]
The various fish groups taken together account for more than half of the known vertebrates. There are at least 24,600 known species of fish, of which over 23,000 are bony fish, with the remainder being about 850 sharks, rays, and chimeras and about 85 hagfishes and lampreys. [9] They range in size from the 16 m (51 ft) whale shark to a 8 mm (just over ¼ of an inch) long stout infantfish.
Many types of aquatic animals commonly referred to as "fish" are not fish in the sense given above. These include cuttlefish, jellyfish, inkfish, and starfish. Marine invertebrates that are consumed as food are commonly called shellfish. Whales and dolphins have been called fish as well, although they are mammals. This usage is no longer common in English
What is a fish?
The term "fish" is most precisely used to describe any non-tetrapod chordate, i.e., an animal with a backbone but lacking four limbs (or having ancestors that had four limbs). Unlike groupings such as birds or mammals, fish are not a single clade but a paraphyletic collection of taxa including hagfishes, lampreys, sharks, rays, lungfishes and coelacanths, sturgeons, gars, and advanced ray-finned fishes. [1]
A typical fish is cold-blooded; has a streamlined body that allows it to swim rapidly; extracts oxygen from the water using gills; has two sets of paired fins, one or two dorsal fins, an anal fin, and a tail fin; has jaws; has skin that is covered with scales; and lays eggs that are fertilised externally.
Fish come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. Their leaf-like appendages enable them to blend in with floating seaweed
However, to each of these there are exceptions. Tuna and some species of sharks are warm-blooded, and able to raise their body temperature significantly above that of the ambient water surrounding them. [2] Streamlining and swimming performance varies from highly streamlined and rapid swimmers which are able to reach 10-20 body-lengths per second (such as tuna, salmon, and jacks) through to slow but more manoeuvrable species such as eels and rays that reach no more than 0.5 body-lengths per second. [3] Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Lungfish have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many catfish, such as Corydoras extract oxygen via the intestine or stomach. [4] Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms as seahorses, pufferfish, anglerfish, and gulpers. Similarly, the surface of the skin may be naked (as in moray eels), or covered with scales of a variety of different types usually defined as placoid (typical of sharks and rays), cosmoid (fossil lungfishes and coelacanths), ganoid (various fossil fishes but also living gars and bichirs, cycloid, and ctenoid (these last two are found on most bony fish. [5] There are even fishes that spend most of their time out of water. Mudskippers feed and interact with one another on mudflats and are only underwater when hiding in their burrows. [6] The catfish Phreatobius cisternarum lives in waterlogged leaf litter [7], [8]
The various fish groups taken together account for more than half of the known vertebrates. There are at least 24,600 known species of fish, of which over 23,000 are bony fish, with the remainder being about 850 sharks, rays, and chimeras and about 85 hagfishes and lampreys. [9] They range in size from the 16 m (51 ft) whale shark to a 8 mm (just over ¼ of an inch) long stout infantfish.
Many types of aquatic animals commonly referred to as "fish" are not fish in the sense given above. These include cuttlefish, jellyfish, inkfish, and starfish. Marine invertebrates that are consumed as food are commonly called shellfish. Whales and dolphins have been called fish as well, although they are mammals. This usage is no longer common in English
